The William J. McCallion Planetarium was the first planetarium in Ontario which offered shows to the public. The original projector was purchased in 1949 from money raised through public subscription and donations from the Royal Astronomical Society of Canada, Hamilton Centre. In the early days, a war-surplus parachute was suspended from the ceiling and used as the planetarium dome. In 1954, the original projector found more permanent accommodation in a custom-designed room in what is now called the Burke Science Building. The first projector was donated to Mount Allison University and replaced with a Spitz model A2 projector in 1961. In 1992, the Ontario Science Centre, in cooperation with the London Children’s Museum, donated a more modern and sophisticated Spitz A3P projector to McMaster. In 2008, the newly-refurbished planetarium re-opened with a Digitarium Alpha 2 system – the first digital projector housed in the McCallion Planetarium. In 2024, the system was upgraded to the current Digitarium Theta 2 system.

The planetarium is named after William J. McCallion, in recognition of his central role in the development of the planetarium at McMaster. Over the years, it is estimated that he gave presentations to as many as 100,000 people. He also served as Director of Educational Services and Dean of the School of Adult Education while at McMaster.